1. Field of the Invention
This invention relates to a collapsible lens barrel suitable for use in a camera.
2. Related Background Art
Heretofore, a lens barrel of this kind has had its full length in the direction of its optical axis shortened (hereinafter referred to as "collapsing") during non-photographing to thereby improve the portability of the lens barrel. Generally, there are two kinds of methods of effecting the collapsing of a lens barrel.
A first method is a method of separating a lens barrel into a mounting portion for a camera body and a barrel portion. The barrel portion is mounted on the camera body in the mounting portion, and the barrel portion is slidable in the direction of the optical axis relative to the mounting portion. During photographing the barrel portion is disposed so as to protrude forwardly of the lens (forwardly of the optical axis), and during non-photographing the barrel portion is retracted to the interior of the camera body, whereby collapse is effected.
A second method is a method used in a zoom lens barrel or the like, and the operation range of an operating ring for driving a zoom lens unit is extended rearwardly of the optical axis. When collapsing is to be effected in this method, the zoom lens unit is moved rearwardly of the optical axis usually beyond a photographing range to thereby shorten the full length of the lens barrel.
However, lens barrels using the above-described conventional collapsing methods have suffered from the following problems.
In a lens barrel using the first collapsing method, if it is a lens barrel equipped with only a function independent on a camera body such as manual focusing or a preset aperture, it is relatively easy to effect its design and manufacture. However, in the case of a lens barrel equipped with the auto focusing function and an automatic aperture mechanism which are now more popular, the presence of an aperture transmitting member and an auto focus drive force transmitting mechanism connected to the camera body side prevents the lens barrel from being simply separated into a mounting portion and a barrel portion. This has led to the problem that the design and manufacture of the lens barrel are difficult.
Also, there are a mirror and others in the camera body and the lifting or the like of the mirror is effected in advance by a discrete mechanism provided on the camera body side, whereafter it is required to retract the barrel portion into the camera body. However, if in the case of lens interchange, the mirror lifting operation is not effected from carelessness, the barrel portion in its collapsed state will strike against the mirror or the internal mechanism of the body and lens interchange will not be effected smoothly. If in contrast, design is made such that the lifting of the mirror takes place automatically during lens interchange, it has led to the problem that the mechanism on the camera body side will become very complicated.
On the other hand, in the case of a lens barrel using the second collapsing method, it is possible to effect collapse only within a range in which a zooming lens unit or the like can be rearwardly retracted. Accordingly, this has led to the problem that in a lens barrel wherein a fixed lens unit is arranged long in the direction of the optical axis, there is a limit to the shortening of the full length of the lens barrel by collapsing.